1. Field of the Invention
The present invention relates to a structure or fixture for fixing a steering column which constitutes a part of a vehicle steering system, relative to a vehicle body, in such a manner that the steering column is movable in the event of application of a load thereto which load is larger than a threshold.
2. Discussion of Related Art
A steering column constituting a part of a vehicle steering system is fixedly supported by a portion of a vehicle body such as a reinforcement of an instrument panel. Although the steering column should be firmly supported by the portion of the vehicle body with a high rigidity, it is desirable that the steering column is supported to be movable upon application of a load thereto whose amount corresponds to a predetermined amount, namely, the steering column is removable from the portion of the vehicle body in the event of a secondary collision between a vehicle's operator and a steering wheel which could occur as a result of a primary collision between the vehicle and another object. It is common that the steering column is fixed to the portion of the vehicle body by means of a fastening structure arranged to fasten a column side member linked to the steering column, to a vehicle-body side member linked to the portion of the vehicle body. The fastening structure is provided with an arrangement permitting the column to be movable relative to the vehicle body. Examples of the structure having such an arrangement are disclosed in JP-3431821B2 (Japanese Patent issued in 2003) and JP-2000-335430A (Japanese Patent Application laid open in 2000).
JP-3431821B2 discloses a structure in which a disk spring is used. A disk spring, in general, is capable of advantageously providing a relatively large “clamping force” (which may be referred also to as “clamping load”), in spite of its relatively small size, and accordingly serving as a preferable component constituting the structure for fixing the steering column relative to the vehicle body. However, the disk spring used in the structure of JP-3431821B2 has a sinuous shape in its axial cross section, and its complicated shape provides difficulty in its manufacturing process and increases its manufacturing cost. In this structure, therefore, there is still room for improvement enabling the structure to be more easily manufactured at a lower cost. This problem is merely one of the problems encountered in conventional structures each using a disk spring, and the conventional structures can be subjected to studies which are to be made in view of various aspects, for improving their practicability.